This invention relates to a flameholder for use in a thrust augmentor in a high performance jet aircraft engine. In particular, the flameholder of the present invention is designed and formed in a single piece of metal.
FIG. 1 is a modified cross-sectional diagram of the thrust augmentor section of a high performance jet engine, usually used in military aircraft. It should be noted that the figure is a modified cross section in that the figure shows only structures which adjoin the central cross-sectional plane, and does not illustrate structures which would normally be viewed beyond that plane. The modified cross-section is used in FIG. 1 and other cross-sectional figures in this application for simplicity of illustration.
The thrust augmentation combustion chamber 10, or augmentor chamber, which is illustrated in FIG. 1 is aft of the engine turbine 12 and surrounds the engine tail cone 22. The augmentation chamber 10 is enclosed by an augmentation duct 14 which is typically a cylindrical structure that contains the augmentor. The augmentor duct 14 serves as a pressure vessel, confining the pressures and directing the flow into the nozzle 25. Within the augmentor duct 14 is arranged an augmentation liner 16 which is a shield that provides thermal protection to the augmentor duct 14 and also acts as an acoustical damper. The augmentation liner 16 extends from the aft end of the turbine to the exhaust nozzle 25. The spacing of the augmentation liner 16 relative to the augmentor duct 14 provides a separate flow of cool fan stream air along the duct inner surface. This air is picked up by the leading edge side of the augmentation liner 16. The rear sheet-metal section of the augmentor duct 14 is extended aft of the liner to obtain a controlled cooling air gap behind the liner for a greater distance. Fuel is supplied to the augmentor by spray rings 18 which are circular in configuration and provide fuel to air entering the augmentor chamber 10. A thrust augmentor flameholder 24, also of circular design and an igniter 20 are arranged behind the spray rings 18 to create turbulence for mixing the fuel injected by the spray rings 18 with the air entering the augmentor chamber and to provide a specific location for combustion which is ignited by the igniter 20.
FIGS. 2 and 3 illustrate a known construction technique for a thrust augmentor flameholder 24. The FIG. 2 view is an axial view of the flameholder 24 from the air inlet end of the engine. FIG. 3 is a modified cross-section taken along the lines illustrated in FIG. 2. The known flameholder 24 includes a pilot gutter, or pilot burner ring 26 which is toroidal in configuration and comprises a U-shaped cross-section member with a circular configuration around the engine axis. Radial inner and outer gutters are formed on sub-assemblies 28 and 30 as shown in FIG. 3, wherein, typically, outer radial gutter 32 is joined to a saddle member 38 by weld 42 and inner radial gutter 36 is joined to saddle member 38 by weld 40. The sub-assembly 30 is then rivetted to the pilot gutter 26 at seam 44 to create with sub-assemblies 28 at other locations as shown in FIG. 2 the flameholder assembly 24 shown in FIG. 2. The flameholder 24 propagates combustion of the fuel entering from the spray rings 18. In particular, the fuel injected by the spray rings 18 impinges on the upstream side of the flameholder 24, that is, from the left side as shown in the view of FIG. 1. The atomized fuel flows around the pilot gutter 26 of the flameholder 24 and is directed to the eddy behind the pilot gutter 26 and carried to the interior of the duct where the igniter 20 produces the ignition of the pilot fuel-air mixture. The flame propagates around the annular pilot burner ring and into the inner and outer radial gutters.
It is an object of the present invention to provide an improved flameholder design characterized by substantially one piece construction, that can provide reduced manufacturing cost and increased durability and performance.